For examining the transmission properties of objects, it is known to illuminate the sample both by an excitation light source, also referred to as a pump light source, and by an illumination light source, also referred to as a sample light source. The light can be visible light or non-visible light. In the process, the molecules of the object under examination are excited by the excitation light source so that the population density of the basic state of the molecule is reduced. By use of the illumination light source, the condition of the molecules can be analyzed in different manners. For instance, there is known the possibility to select the wavelength of the illumination light source to be similar to that of the excitation light source. This has the consequence that the radiation coming from the illumination light source will not be taken up anymore by the already excited molecules and thus, under the influence of the excitation radiation, the transmission of the illumination radiation through the object is increased. On the other hand, the wavelength of the illumination radiation can be selected to be similar to the emission wavelength of the excited molecules. In this case, the illumination radiation can cause the stimulated emission of photons in the molecules excited by the excitation radiation. This will result in a seemingly increased transmission of the illumination radiation because of the occurrence of additional photons emitted in the object which have the same wavelength. A further known possibility resides in selecting the wavelength of the illumination radiation to the effect that the wavelength can be preferably absorbed by such molecules which are already in the condition excited by the excitation radiation. In this case, the excitation of the molecules by the excitation radiation will effect a decrease of the transmission of the illumination radiation. In the known methods, both the illumination light source and the excitation light source are focused at the same site on the object. In this case, to be able to use a common optics system, both light sources are arranged on the same side of the object. A detector device is located on the opposite side of the object for measuring the transmission.
To make it possible to perform a three-dimensionally spatially resolved measurement within an object, a confocal configuration is of advantage. In this regard, a variety of optical arrangements are known:
In confocal microscopy where typically only one light source is used, it is known to arrange an optics system and a pinhole in front of the detector and to adjust them in such a manner that the detector will preferably receive light from that measurement volume which also lies in the focus of the light source. In such an arrangement, the illumination radiation and the detection radiation are guided through the same optics system.
It is also known, in case that separate excitation and illumination light sources are used, that these light sources can be focused by a common optics system onto a common measurement volume. As a result of the preferred illumination of the measurement volume by both light sources, the three-dimensional spatial resolution of the measurement will be guaranteed already on the side of the illumination; in this case, the detector does not necessarily have to be a spatially resolving detector. However, this arrangement suffers from the basic disadvantage that a parallelized measurement, i.e. a simultaneous measurement of a plurality of measurement volumes in the object, is not possible because the detector will always capture the light of all measurement volumes together and a spatial assignment will not be possible.
It is an object of the invention the provide a device and a method for measuring optical properties of an object, preferably for measuring the optical transmission properties of the object, which method and device make it possible to perform a parallelized measurement of a plurality of measurement volumes.